wwPDB Policies and Processing Procedures
Document
Section B: wwPDB processing procedures
Authored by the wwPDB annotation staff
January 2024 Version 4.4
Table of Contents
Preface
1. Entry title, authors, and citation information
2. Macromolecule information
3. Polymer sequences and sequence database reference assignment
4. Ligands
5. Coordinate section
6. Chain ID assignment
7. HEADER assignment
8. Assembly
9. Miscellaneous records
10. Structural Genomics Entries
11. Information specific to X-ray structures
12. Information specific to NMR structures
13. Information specific to Electron Microscopy structures
14. Viral capsids and other complex assemblies
15. Re-refinement of another author's data
Appendices:
A. HEADER list
B. Format for Structure Factors

Preface
Since 1999, the wwPDB has been responsible for processing PDB data with deposition
centers at RCSB PDB, PDBe, and PDBj. The processed entries follow the mmCIF format
that complies with the PDB Exchange Dictionary (PDBx)
https://mmcif.wwpdb.org/dictionaries/mmcif_pdbx_v50.dic/Index/
The version of the PDB file and its correspondence to the file format guide will be included
in all files processed and released by the wwPDB.
This document presents the current processing procedures. The wwPDB staff will continue toupdate annotation practices in line with evolving structure determination and annotation
methods.
December 2008: Initial release as version 2.2
March 2009: minor revision 2.3, updates on citation, header list, SITE records and added cif
templates for structure factors.
April 2009: minor revision 2.4, update header list.
November 2011: major revision 2.5, clarify content, update header list and UniProt sequencesubmission.
December 2012: Clarify Entry title.
January 2014: Clarify Re-refinement.

August 2017: Clarify Best representative conformer of NMR entries.
May 2018: Update biological assembly annotation procedure.
July 2021: major revision 4.0 to clarify content and provide examples in mmCIF format.
November 2021: IDs reserved for new ligand used in structure determination process
November 2022: Peptide bonds in polymer chain need to be in same direction
November 2023: Distinct chain IDs for cleaved polymer chains
January 2024: Restriction of chain ID length

1. Entry title, authors, and citation information
Entry Title (_struct.title)
Entry titles should be descriptive and match the content of the entry. PDB staff may modify
the entry title during data processing or before entry release if the title is ambiguous or does
not match the content of the structure.
Authors may choose to suppress the information about the entry authors and title so that it
does not appear on the PDB website until the entry is released to the public.
Author information ( _audit_author.name)
The authors for a PDB entry can be the same as the authors for the primary citation, or asubset of citation authors. Alternatively, there may be more authors listed for the entry
compared to the citation author. Generally, at least one of the authors for the entry should be
included in the author list for the primary citation.
The authorship of the entry is at the discretion of the principal investigator (PI). If more than
one PI is responsible for the entry, they will need to come to a mutual decision on theauthorship.
Citation information
Authors are encouraged to deposit their structures in advance of publication. The primarycitation is the paper that describes the structure in the PDB entry.
ThesisConference Proceedings and Thesis can only be included as primary citation, but not insecondary citations.
PubMed Ids
PubMed IDs are available for the primary citations of entries in the PDB, mmCIF and XML
files. When available, DOI numbers are also included.
Patents
Patent IDs can be recorded (_citation.pdbx_database_id_patent), and the journal name will be‘Patent’.
Unpublished structures
If the author indicates that the entry will never be published, a journal name of 'not published'
will be added to citation.journal_abbrev records.
Jr.
Journal and entry author names that have the suffix "junior" will be represented as "Jr." andnot as "junior", for example, ‘Smith Jr., J.’.
Title case
All titles, names etc. are included in mixed case in the mmCIF format file to match theliterature.

2. Macromolecule information
How are the macromolecule names and synonyms assigned?
Protein molecule names
Protein molecule names and synonyms are standardized to be consistent with thecorresponding UniProt entry and are listed in the _entity.pdbx_description and_entity_name_com.name records. The exceptions are as follows:• If the UniProt name refers to a precursor and the entry contains mature protein, theword precursor will not be included in the protein name. If the author did indicate
putative, then the wording will be retained.
• In the case of zymogens, if the UniProt name is "trypsinogen" but the activatedprotein is present in the structure, then "trypsin" is used as the name.
• If the UniProt entry contains the complete gene sequence of a protein that is processed
into more than one chain, the corresponding polypeptide name will be given as thename in the PDB entry. For example, if the UniProt name is insulin, the protein names
correspond to the chain names: such as Insulin A chain and Insulin B chain.
• For viral proteins, where a polyprotein is synthesized, and where the PDB entry
contains all the components, the name polyprotein can be used. Otherwise, the nameof the fragment from UniProt will be used. For example, if a "genome polyprotein" iscomposed of capsid, envelope protein, and major envelope proteins but the deposited
structure is only of the envelope protein, the name used will be "envelope protein".
• If the full UniProt sequence for the protein is not present in the sample, the fragment
section will be filled in. However, the fragment section will not be filled in wherecomplete mature protein is represented, for example for a complete trypsin moleculeor envelope protein etc.
• If the UniProt name is not assigned (i.e., it is "hypothetical") and the author has aname for the protein, the author's protein name will be used.
• If the author's name for the molecule differs from the UniProt molecule name, theUniProt primary name will be used for the molecule name. The author's molecule
name will be listed first in the synonyms list, followed by the synonyms provided in
UniProt.
• If there is no corresponding UniProt entry, the author provided protein name will be
used.
• Antibodies will be named using as much information as the author provides.
Examples:i.
Fab fragments will be named as Fab heavy chain and Fab light chain.
ii.
For immunoglobulin G chains (which include fab and fc regions), the proteinnames will be "antibody heavy chain" and "antibody light chain."iii. If the author provided specific names for the antibody, then those names will
be used e.g., Fr62 monoclonal antibody light chain and Fr62 monoclonal
antibody heavy chain.
• For chimeric proteins, the protein name is comma separated and may refer to thepresence of a linker (protein_1, linker, protein_2). Other details about the chimera canbe provided in entity.details and pdbx_entry_details.sequence_details.
Nucleic acid molecule names
For all nucleic acid sequences, biological names should be used when available. The
biological name is either provided by the author or it is obtained from a sequence database,such as "16S RIBOSOMAL RNA".

If the sequence is shorter than 24 nucleotides and no biological name is available, themolecule name is given as the short sequence:5'-D(*CP*GP*CP*GP*(8OG)P*AP*TP*TP*CP*GP*CP*G)-3'
For sequences equal to or greater than 24 nucleotides, when no biological name is available,
the name may be listed as “50-mer RNA”, for example.
Carbohydrate polymers
As of July 2020, the rules we apply for entries containing carbohydrate polymers are thefollowing:(1) Residues are ordered from the reducing to non-reducing end. For common glycosylation,
there is only one reducing end, with branches at non-reducing end. This is like a tree, whereordering always starts from the root (reducing end), because it's inconsistent to count fromthe ends of branches (non-reducing end).
(2) The longest branch is taken as main branch. If two branches have the same length, thenthe lower locant goes first. This is to follow 1996 IUPAC/IUBMB recommendation.
For more information, please consult https://www.wwpdb.org/documentation/carbohydrateremediation
How is fragment information indicated? (entity.pdbx_fragment)
If the PDB entry contains a fragment of the protein in the sequence records when comparedto the UniProt entry, the fragment name can be included, for example: N-terminal domain, Cterminal domain, catalytic domain, ligand binding domain, etc.
How is the E.C. number assigned (entity.pdbx_ec)?
The E.C. number is automatically extracted from the UniProt entry. If the UniProt entry does
not have an E.C. number information, the author’s provided information will be used. If theauthor disagrees with the UniProt assignment of E.C. number, the wwPDB staff will contact
the UniProt staff and try to clarify the discrepancy. In the case where the matter cannot be
resolved, the author provided E.C. information can be added to the entity.details andindicated as "Author provided E.C. number is xxxx".
How are mutations indicated (_entity.pdbx_mutation)?
The exact mutation will be described in the mmCIF file in the following manner: Y20K. The
sequence difference records (struct_ref_seq_dif) will contain a corresponding record with theannotation "ENGINEERED MUTATION".
How is the macromolecule source organism indicated?
The source organism is identified by its scientific name and taxonomy id as listed in the
NCBI Taxonomy database. During entry annotation the official scientific name is usuallyobtained from UniProt database which is based on the NCBI Taxonomy database. The source
organism name and taxonomy id will be listed under _entity_src_nat mmCIF category if thepolymer molecule was naturally obtained, under _entity_src_man if it was geneticallymanipulated (expressed) and under _pdbx_entity_src_syn if it was chemically synthesized.
If a common name is listed in the NCBI taxonomy database, then the common name ismapped to the _entity_src_gen.gene_src_common_name field, otherwise this will be left
blank. The scientific name of the source and host organisms, plasmid and gene names will be
included in mixed case to match the standard scientific literature.
The source organism names of each part of a chimeric protein are listed in the mmCIF files
with corresponding residue ranges.
For example:

loop__entity_src_gen.entity_id_entity_src_gen.pdbx_src_id_entity_src_gen.pdbx_alt_source_flag_entity_src_gen.pdbx_seq_type_entity_src_gen.pdbx_beg_seq_num_entity_src_gen.pdbx_end_seq_num_entity_src_gen.gene_src_common_name_entity_src_gen.gene_src_genus_entity_src_gen.pdbx_gene_src_gene_entity_src_gen.gene_src_species_entity_src_gen.gene_src_strain_entity_src_gen.gene_src_tissue_entity_src_gen.gene_src_tissue_fraction_entity_src_gen.gene_src_details_entity_src_gen.pdbx_gene_src_fragment_entity_src_gen.pdbx_gene_src_scientific_name_entity_src_gen.pdbx_gene_src_ncbi_taxonomy_id_entity_src_gen.pdbx_gene_src_variant_entity_src_gen.pdbx_gene_src_cell_line_entity_src_gen.pdbx_gene_src_atcc_entity_src_gen.pdbx_gene_src_organ_entity_src_gen.pdbx_gene_src_organelle_entity_src_gen.pdbx_gene_src_cell_entity_src_gen.pdbx_gene_src_cellular_location_entity_src_gen.host_org_common_name_entity_src_gen.pdbx_host_org_scientific_name_entity_src_gen.pdbx_host_org_ncbi_taxonomy_id_entity_src_gen.host_org_genus_entity_src_gen.pdbx_host_org_gene_entity_src_gen.pdbx_host_org_organ_entity_src_gen.host_org_species_entity_src_gen.pdbx_host_org_tissue_entity_src_gen.pdbx_host_org_tissue_fraction_entity_src_gen.pdbx_host_org_strain_entity_src_gen.pdbx_host_org_variant_entity_src_gen.pdbx_host_org_cell_line_entity_src_gen.pdbx_host_org_atcc_entity_src_gen.pdbx_host_org_culture_collection_entity_src_gen.pdbx_host_org_cell_entity_src_gen.pdbx_host_org_organelle_entity_src_gen.pdbx_host_org_cellular_location_entity_src_gen.pdbx_host_org_vector_type_entity_src_gen.pdbx_host_org_vector_entity_src_gen.host_org_details_entity_src_gen.expression_system_id_entity_src_gen.plasmid_name_entity_src_gen.plasmid_details_entity_src_gen.pdbx_description
1 1 sample 'Biological sequence' 1
121 ? ? ? ? ? ? ? ? ? 'Mus musculus'
10090 ? ? ? ? ? ? ? ? 'Escherichia coli' 562 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ?
1 2 sample 'Biological sequence' 122 172 ? ? ? ? ? ? ? ? ? 'Homo sapiens'
9606 ? ? ? ? ? ? ? ? 'Escherichia coli' 562 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ?

If an expression system was used, the scientific organism name of the expression system will
also be taken from the NCBI Taxonomy database and listed under_entity_src_gen.pdbx_host_org_ncbi_taxonomy_id records.

Other information about the source and expression system is not mandatory and will be
included in the file only if the author has provided it.
Phage display
The _entity_src_gen category will be populated with the organism where the gene sequence
was first isolated and the host organism of the overexpression system used to generate thefinal protein. Additional information about phage display can be mapped to_entity_src_gen.pdbx_description for example: ’Protein selected by phage display’.
Cell-free synthesis, in vitro transcription and in vitro translation
Cell-free synthesis, in vitro transcription and in vitro translation will all be described as "cellfree synthesis". Common cell extracts in use today for cell-free protein production are madefrom E. coli (ECE), rabbit reticulocytes (RRL), wheat germ (WGE), insect cells (ICE) andYeast Kluyveromyces (the D2P system). All will have genetically manipulated sources(_entity_src_gen category) populated with the above-mentioned source organisms and therelevant taxonomy ids. Other information about the synthesis, such as "cell-free synthesis"
can be added to the _entity_src_gen.pdbx_description.
Baculovirus
If a baculovirus was used, it would be listed under the vector type. If a cell line is provided, it
will be added to the entry.
Synthetic
The term "synthetic" means "synthesized using non biological methods". Taxonomy ID for
synthetic source is 32630.
Undefined
This term is used for cases when the source organism cannot be identified. Taxonomy ID for
undefined source is 32644.

3. Polymer sequences and sequence database reference assignment
What is the definition of polymer sequence (entity_poly, SEQRES)?
The polymer sequence is a list of the consecutive chemical components covalently linked in a
linear fashion to form a polymer. The chemical components included in this listing may be
standard or modified amino acid or nucleic acid residues. It may also include other residues
that are linked to the standard backbone in the polymer. Chemical components or groups
covalently linked to the side chains of peptides or groups linked to sugars and/or bases innucleic acid polymers will not be listed here.
Proteins containing three or more residues, forming two consecutive standard peptide bonds,
in the same direction will be assigned polymer sequence records (molecule name, source,
sequence, sequence database reference).
Nucleic acids containing two or more residues linked by standard nucleotide bonds will beassigned polymer sequence records (molecule name, source, sequence, sequence databasereference).
The polymer sequence records must represent the complete sequence of each sample used in
the experiment, including any expression tags, and residues not modelled in the coordinates(for example unobserved regions due to local disorder). Residues cleaved from the polymer
sequence prior to or during the experiment are not considered part of the sequence. The
polymer sequence can include neighboring cross-linked residues (such as chromophores) andmodified amino acids.
What if the exact sequence of the sample is not known?

If the exact sequence of the sample is not known, due to, for example, proteolysis, thesequence should match the coordinates and a dedicated sequence remark(_pdbx_entry_details.sequence_details, REMARK 999) with an explanation should be added.
In such cases if the entry is a crystal structure, Matthew's coefficient and solvent content will
list author-provided values instead of calculated values.
What is the sequence database reference (_struct_ref, _struct_ref_seq, DBREF)?
The sequence database reference provides the mapping between polymer sequences and avalid sequence database reference.
Which polymer chains are assigned sequence database records?
Each protein or nucleic acid chain, for which there is an appropriate sequence database match
will list cross references to the sequence database entry. When no sequence databasereference is available the sequence will be self-referenced (i.e., the database reference will be
the PDB entry itself).
Which sequence databases will be used?
• Proteins
UniProt is the current preferred protein sequence database. Where there are multiple
UniProt entries for the same protein from the same organism, strain and sequence
identity, the UniProt entry that has the most annotation will be used. Also, UniProt
entries that contain the complete protein sequence will be preferred over those that
represent protein fragments.
• Nucleic acids
Naturally obtained nucleic acid sequences can be referenced to GenBank.
• Non-ribosomal peptides
NORINE database was used for some sequence database references. The reference to
NORINE is currently discontinued. UniProt reference (if available) or self-referenceis used instead.
• DNA and RNA
All DNA will be self-referenced. RNA polymers more than 50 residues long, will be
provided GenBank sequence reference if available.
What if a UniProt reference is not available for a protein sequence?
UniProt does not contain variable or hyper-variable regions of the immune system or
unnatural sequences, so the PDB entries for such structures will be self-referenced. If theprotein does not fall into these categories and does not have a UniProt reference, UniProt
automatically obtains sequences from the PDB and adds them to UniProt.
What if a UniProt reference has become available or has been changed in the UniProt
database for a protein sequence?
The PDB entry contains the sequence cross reference available at the time of processing of
the entry. If at a point in the future the sequence does appear in UniProt or if a UniProt
accession code has been changed, the updated version of the sequence database match will beavailable to users through the SIFTS project. The PDB entry may not be modified to
add/update the sequence cross-reference. Information about SIFTS is available fromhttps://www.ebi.ac.uk/pdbe/docs/sifts/
If related entries with the same sequence do not have UniProt references, the sequencereference will refer to each PDB entry itself and not refer to the first PDB entry whichcontained the particular sequence. For example, if entries 1ABC, 1DEF and 1GHI all havethe same antibody sequence, these entries will refer to 1ABC, 1DEF and 1GHI, respectively.
How are chimeras handled?
Chimeras or fusion proteins should be deposited as a single chain with one chain ID because
they were expressed as one chain. Chimeras that were refined with different chain IDs should
be deposited with one chain ID for all parts of the chimera, including any linker regions.
The sections of the chimera which match the UniProt entry or entries will each have databasereferences. The sections of the chimera which do not match the UniProt entry or entries, will
be self-referenced.
What is the sequence reference difference (_struct_ref_seq_dif, SEQADV)?
The sequence difference records describe any rational disagreement between a sequence
database and the sequence in the PDB entry.
What are the various types of sequence differences and how are they annotated?
• Engineered mutation: Difference between the PDB sequence and the UniProt entry
that were engineered will be listed as “engineered mutation”.
• Cloning artifact: The term cloning artifact is reserved for instances where a sequence
difference is introduced, as in a PCR experiment during cloning or by random
mutation. These instances are rare.
• Modified residue: Only instances where the parent of a modified residue does notmatch the sequence database reference will be listed here. For example, if THR islisted in the UniProt entry, and the PDB residue is MSE (selenomethionine), thenstruct_ref_seq_dif (SEQADV) record for MSE/THR with the explanation of"engineered mutation" will be generated, all other cases of modified residues will belisted under pdbx_struct_mod_residue (MODRES) records.
• Microheterogeneity: See section “How is microheterogeneity/polymorphism
handled?” below.
• Chromophore: See section "Neighboring intra-chain cross-linked groups" below.
• Conflict: Sequence conflicts between a residue in the polymer sequence and that
listed in the UniProt reference that cannot otherwise be explained, will be listed herewith the explanation of "conflict" and additional sequence details may also be
provided.
• Expression tag: Extra N- and/or C-terminal residues including leader sequences, Histags, other kinds of tags and/or initiating methionine(s).
• Insertion: in the middle of the sequence that is not part of the UniProt sequence• Deletion: where the construct of the protein in the middle of sequence that has the
UniProt reference is deleted.
• Linker: a region in sample sequence linking partitions of a chimeric entity.
What sequence differences are not listed?
• Polymers which do not have a UniProt reference (self-referenced).
• Modified residues where the parent residue matches the database reference.
MODRES records (_pdbx_struct_mod_residue) will be created for modified residues
if the residue is derived from a parent residue. For instance, MSE (selenomethionine)
will only have a pdbx_struct_mod_residue (MODRES) entry when Met is listed in the
UniProt entry.
• D-amino acids

How is microheterogeneity/polymorphism handled?
Polymer chains which have the same sequence must have the same chemistry(homogeneous). If one chain has microheterogeneity at one position, but not in another chainat the same position, then these two polymer chains will be treated as two different polymer
entities with two sequences. If a residue has more than one identity at a particular position
within a chain, this is called microheterogeneity.
For heterogeneous chains, the residue which does not match the corresponding UniProt
residue will be listed in the sequence, regardless of its occupancy. The total sum ofoccupancies of the different identities of the residues that display microheterogeneity shouldbe less than or equal to 1.
If none of the residue identities match the UniProt residue at the corresponding sequence
location, the residue with the higher occupancy will be listed in the sequence.
A sequence difference record will be generated for the difference between the UniProt
sequence and the polymer sequence, with the explanation of "microheterogeneity". If there is
no UniProt reference, the higher occupancy residue will be listed in the sequence and nosequence difference records will be generated.
If a residue has two identities at a particular residue number, where one identity is a modified
residue and one is the unmodified form, then the modified residue will be listed in thepolymer sequence, and a "microheterogeneity" record will be generated in the sequence
difference category. This is the exception to the rule that sequence difference records would
not be created for modified residues.
Alternate position indicators will be used in the coordinates for residues involved in
microheterogeneity. The residue listed in the polymer sequence will be listed first in thecoordinates and be labeled as alternate position identifier A. The other identity will beassigned alternate position identifier B. If there is a third or fourth residue identity, or if oneof the identities has its own alternate conformations, these will be assigned alternate IDs inalphabetical order.
In the mmCIF file, all residue identities involved in microheterogeneity and a
microheterogeneity flag will be listed in _entity_poly_seq.hetero and_poly_seq_scheme.hetero.
Example (PDB entry 5ZA2):
loop__entity_poly_seq.entity_id_entity_poly_seq.num_entity_poly_seq.mon_id_entity_poly_seq.hetero...
2 56 ILE n 2 57 GLY n 2 58
2 58 SER y 2 59 VAL n 2 60
...

SEP y
SER n

loop_
_pdbx_poly_seq_scheme.asym_id_pdbx_poly_seq_scheme.entity_id_pdbx_poly_seq_scheme.seq_id_pdbx_poly_seq_scheme.mon_id_pdbx_poly_seq_scheme.ndb_seq_num_pdbx_poly_seq_scheme.pdb_seq_num_pdbx_poly_seq_scheme.auth_seq_num_pdbx_poly_seq_scheme.pdb_mon_id_pdbx_poly_seq_scheme.auth_mon_id_pdbx_poly_seq_scheme.pdb_strand_id_pdbx_poly_seq_scheme.pdb_ins_code

_pdbx_poly_seq_scheme.hetero...
B 2 56 ILE 56 62 62 ILE ILE B . n
B 2 57 GLY 57 63 63 GLY GLY B . n
B 2 58 SEP 58 64 64 SEP SEP B . y
B 2 58 SER 58 64 64 SER SER B . y
B 2 59 VAL 59 65 65 VAL VAL B . n
B 2 60 SER 60 66 66 SER SER B . n...

A full explanation of the microheterogeneity for all residues at a particular residue number
may be further elaborated with additional sequence details text remark.
Neighboring intra-chain cross-linked groups
This section describes cases of neighboring intra-chain cross-linked typically involving 2 ormore sequential amino acids that react with each other to form one "residue". For example,
residues 65, 66, and 67 in the PDB entry 1yjf underwent a reaction to form a circularized tripeptide chromophore (Figure 1).

Figure 1: In entry 1yjf, residues 65, 66, and 67 (neighboring alanine, serine and glycine
residues) reacted and generated a chromophore product called [2-(1-AMINOETHYL)-4METHYLENE-5-OXO-4,5-DIHYDRO-1H-IMIDAZOL-1-YL]ACETIC ACID.
To describe this situation in a PDB entry the following annotation applies:• The neighboring intra-chain cross-linked group will be listed as one chemical group in
the coordinates and in the sequence.
• The neighboring intra-chain cross-linked group will have three parent residues, if
three amino acids were involved in the reaction to make the chromophore. Thus, there
will be three pdbx_struct_mod_residue (MODRES) records.
• There will be struct_ref_seq_dif (SEQADV) record(s) generated with the explanation"chromophore". Any additional information can be added to
pdbx_entry_details.sequence_details (REMARK 999).

4. Ligands

The wwPDB encourages depositors to provide an InChI or SMILES string and/or chemicalname and/or chemical drawing including bond type, bond order and stereochemistry of theligand in order to facilitate the correct annotation.
How is the identity of a ligand verified?
Specialized software is used to get bond types, stereochemistry, and where possible the
IUPAC-compliant name for each ligand in the structure. Verification is done by comparing to
the ligand structure in the coordinates vs the one defined in the wwPDB ChemicalComponent Dictionary (CCD). When a ligand match is found in the CCD, the atom names in
the coordinates are matched to the dictionary definition.
How is the ligand identity assigned?
Each component (ligand, amino acid, nucleic acid) is assigned a unique code in the CCD.
During curation, annotators use multiple methods to compare components against the CCD.
If stereochemistry, bond types and connectivity match an existing definition in the CCD thenthe existing definition is assigned to the ligand. If there is no match, a new CCD definition isadded to the CCD with an arbitrarily assigned unique identifier.
How are new ligands added to the chemical component dictionary?
To designate the new ligands we encourage the use of the following ids in the structure
determination process: DRG, LIG, INH, 00 - 99 (2 digits). These ids are excluded from the
CCD, and are instead reserved for initial deposition of any ligand that is new to the CCD.
Several software programs are used to generate a CCD definition based on the author's
deposited coordinates. All atoms in the component CIF file (including H-atoms) will havecoordinates. If there are atoms missing from the coordinates due to disorder, they will be
added to the component CIF file. A set of ideal coordinates and an IUPAC-compliant
chemical name will be generated for the complete molecule. Checks for chemical name,ligand code and connectivity are carried out to verify that duplicates are not added to the
CCD.
What happens if a structure contains a ligand that already exists in the chemicalcomponent dictionary?
If a particular ligand in the structure is already defined in the CCD, the ligand 3-letter
identifier, its chemical name and atom nomenclature will be updated according to thedictionary during entry annotation. It is noted that the atom names will always start with theelement type.
Are peptide-like inhibitors treated as ligands?
If a peptide-like inhibitor is a natural product or if it has a sequence database reference, or if
the majority of the residue components are standard or modified amino acids, it is treated as apolymer. Otherwise, the molecule is treated as a ligand.
Charge state
Whenever possible, the overall charge for new ligand definitions should be neutral. This
provides maximum compatibility with other chemical databases such as CAS and PubChem.
The overall charge of the ligand is included in the CCD. The individual atoms may have acharge in the atom records.
Exceptions:•

Tetravalent nitrogen atoms where all four bonding partners are heavy atoms mustcarry a positive charge to satisfy valence rules• Nitro groups (R-NO2) are represented in a charge separated state(R-[N+](=O)[O-]), again, to better satisfy valence rules.
• Organometallic complexes
Ligands in NMR structures produce unique challenges because all hydrogen atoms used in
the structure must be present in the dictionary. The accurate chemical description ofmolecules which may exist in multiple protonation states is difficult to achieve in single
chemical component definitions. To describe this complexity for the standard amino acids
and nucleotides, a special component dictionary has been created(https://www.wwpdb.org/data/ccd). Within this dictionary are complete chemical descriptionsof observed protonation states which include accurate formula, formal charges and IUPAC
atom nomenclature for each case.
How are ligand names and synonyms assigned?
_chem_comp.name (HETNAM) Whenever possible, the name automatically produced by
specialized chemical naming software is used. Exceptions to this rule are common (as judged
by annotation staff) biological names, and brand names for drugs. Should ACDlabs,
Chemdraw or PubChem fail to predict a name, common names or names supplied by thedepositor may be used.
_chem_comp.pdbx_synonyms, _pdbx_chem_comp_synonyms (HETSYN) Other names
requested by depositors may be included as synonyms (_pdbx_chem_comp_synonyms), at
the discretion of the annotator. It should be noted any synonyms provided by the depositor
should be meaningful and widely used names for the ligand.
Exceptions / Issues: Established common names can be used as molecule names as long as
the IUPAC-compliant name is listed as a synonym name. For example, "Fluconazole" can beused as molecule name and "2-(2,4-difluorophenyl)-1,3-bis(1,2,4-triazol-1-yl)propan-2-ol" asa synonym. If a ligand name is changed or synonyms are added, every PDB entry containingthat ligand will be updated.
Metals: There are difficulties in handling dative bonds in coordination complexes and pibonding in organometallic complexes. These inorganic molecules need to be built on a caseby-case basis to reflect their chemical nature. An ambiguous flag(_chem_comp.pdbx_ambiguous_flag) is included in the chemical component files for suchmolecules where current cheminformatics software is inadequate or unable to describe thetrue chemical structure.
A number of ligands that were defined as "metal bound to multiple waters" have been marked
as obsolete (status code of OBS) meaning they are no longer valid ligands, and should not be
used in the future. While water coordinated metals can be strongly bound, these groups are
not consistently used among all structures, and user analysis would benefit fromstandardizing the single ion representation. Entries which contained such ligands were
updated to split them into metal and water molecules.
Leaving groups: In order to accurately represent the polymerization potential of entries in
the chemical component dictionary, all atoms that can be lost from a ligand in the process ofmaking a linkage will be marked with a special flag indicating these are 'leaving atoms'.
For example, standard amino acids have the carbonyl oxygen atom OXT, and the N-terminalhydrogen HN2 are always marked as leaving atoms as these are lost in the process of creatinga polypeptide chain. This, however, does not suggest that these atoms are always missing
from the coordinates, but rather these atoms are invariably missing in a polymeric state
depending on the position and bonding state of the chemical entity.

Portions of ligands that are missing: Ligands are defined as if all atoms were present in theexperiment. If the ligand is only partially seen in the experiment (for example, a ring is
missing in the density for a crystal structure), the ligand code that is used is for the fully
defined ligand. If the ligand is new, the missing atoms are added to the definition of theligand.
Modified amino acids and nucleotides: If an amino acid or nucleotide is modified by achemical group greater than 10 atoms, the residue will be split into two groups: the aminoacid/nucleotide group and the modification. A link record will be generated between theamino acid/nucleotide group and the modification. Modified amino acids and nucleotides will
follow standard atom nomenclature.
Nucleotide residue identifiers: The standard nucleotides are represented using the following
residue identifiers for DNA: DA, DG, DC, DT and the following residue identifiers for RNA:
A, G, C, U.
Use of UNX/UNL/UNK There are times when an amino acid residue, nucleotide, atom, or
ligand is unidentified. These ligand codes should be used in the following cases:• UNX: unknown atom or ion• UNL: unknown ligand• UNK: unknown amino acid• N/DN: unknown nucleotide
UNX UNX is the code for one atom or ion, by itself, when author does not know the identityof that atom or ion. NOTE: The ligand name is UNX, but the atom name is UNK. The atom
type is "X".
UNL UNL is the code for unknown ligands. This is for where author has added atoms to thecoordinates to satisfy the electron density, but true ligand identity is not known. For example,
see PDB entry 3MHO.
UNK UNK is the code for unknown amino acids only. For example, a poly-ALA or polyGLY chain would be processed as poly-UNK, if the author does not know how thecoordinates align with the sequence and the residue numbering is arbitrary. The sequence
would be poly UNK and the residues in coordinates would be listed as UNK. The sequence,
if known, may be listed in the sequence details section. If the authors do know the alignmentof sequence and coordinates, the poly-ALA or poly-GLY residues should be changed tomatch the sequence. The atom names of UNK are N,CA,CB,CG,O,C, and the atom types are
N,C,C,C,O,C.
N/DN is the code for unknown nucleotide where the base is not observed.
What if the ligand identity provided by the depositor conflicts with the software andannotator identification of a ligand?
Conflicts between the author's identification of a ligand and the software and/or annotator
identification of a ligand are brought to the attention of the author. In case of disagreement
between the depositor and the wwPDB staff, the ligand name will be based on what isderived from the coordinates by specialized chemical naming software. If stereochemistry
cannot be determined by a program, the author's description of stereochemistry will be used.
For ambiguous stereochemistry or bond length, _pdbx_entry_details.nonpolymer_details(REMARK 600) and a flag might be added to the mmCIF file.
The Biologically Interesting Molecule Reference Dictionary (BIRD)
The Biologically Interesting molecule Reference Dictionary (BIRD) contains information
about biologically interesting peptide-like antibiotic and inhibitor molecules in the PDB
archive.

BIRD is an external reference file (similar to the CCD) that provides information about thechemistry, biology, and structure of these molecules.
BIRD entries include molecular weight and formula, polymer sequence and connectivity,
descriptions of structural features and functional classification, natural source (if any), andexternal references to corresponding UniProt or Norine entries.
The entire BIRD resource can be downloaded from the wwPDB FTP area:
https://ftp.wwpdb.org/pub/pdb/data/bird/
BIRD is regularly reviewed for consistency and accuracy, and is used to uniformly annotate
PDB entries containing these molecules. The dictionary is updated each week with new
definitions as the corresponding PDB entries are released in the PDB archive.
The corresponding BIRD ID code only appears in the PDBx-formatted file of the entry.
Additional details about BIRD annotation are available at: https://www.wwpdb.org/data/bird

5. Coordinate section
Alternate conformations
How are alternate conformations of individual atoms, side chains, or entire residues
handled?
Sometimes an atom, several atoms, or an entire side chain has more than one conformation.
Each set of coordinates for the atom is assigned alternate position A and B, or if there arethree alternate positions, A, B, and C, etc. The combined occupancies of the alternate
positions should not exceed 1.00. Generally alternate conformation A should have the higher
occupancy.
Exampleloop__atom_site.group_PDB_atom_site.id_atom_site.type_symbol_atom_site.label_atom_id_atom_site.label_alt_id_atom_site.label_comp_id_atom_site.label_asym_id_atom_site.label_entity_id_atom_site.label_seq_id_atom_site.pdbx_PDB_ins_code_atom_site.Cartn_x_atom_site.Cartn_y_atom_site.Cartn_z_atom_site.occupancy_atom_site.B_iso_or_equiv_atom_site.pdbx_formal_charge_atom_site.auth_seq_id_atom_site.auth_comp_id_atom_site.auth_asym_id_atom_site.auth_atom_id_atom_site.pdbx_PDB_model_num...
ATOM1179 C CAA GLU A 1 75 ? 3.108
GLU A CA
1
ATOM
1180 C CAB GLU A 1 75 ? 3.163
GLU A CA
1
…

5.119

18.896 0.58 12.70 ? 167

5.208

18.892 0.42 12.51 ? 167

How are alternate conformations of chemical groups handled?
Chemical group alternate conformations are handled in the same way as amino acids, unlessthe alternate conformations involve two different chemical groups.
What if two different chemical groups are in alternate conformations?
The author may state that two chemical groups are alternate conformations of each other but
have different identities. For example, the author may state that the chemical group at aparticular location is both zinc and copper. Unlike polymorphic residues, ligands cannot be
assigned the same residue number; different residue numbers must be assigned. In thisexample, zinc would be residue 100, and copper residue 101. Zinc would be assigned
alternate conformation A, and copper would be assigned alternate conformation B. The
ligand with the higher occupancy is generally, but not always, assigned alternate
conformation A. The occupancies of each ligand should be less than 1.00 and combined
should be less than or equal to 1.00.
Exampleloop__atom_site.group_PDB_atom_site.id_atom_site.type_symbol_atom_site.label_atom_id_atom_site.label_alt_id_atom_site.label_comp_id_atom_site.label_asym_id_atom_site.label_entity_id_atom_site.label_seq_id_atom_site.pdbx_PDB_ins_code_atom_site.Cartn_x_atom_site.Cartn_y_atom_site.Cartn_z_atom_site.occupancy_atom_site.B_iso_or_equiv_atom_site.pdbx_formal_charge_atom_site.auth_seq_id_atom_site.auth_comp_id_atom_site.auth_asym_id_atom_site.auth_atom_id_atom_site.pdbx_PDB_model_num...
HETATM 2239 C C
A CO2 C 3 .
C
1HETATM 2240 O O1 A CO2 C 3 .
O1 1
HETATM 2241 O O2 A CO2 C 3 .
O2 1
HETATM 2242 C C
B BCT D 4 .
C
1
HETATM 2243 O O1 B BCT D 4 .
O1 1
HETATM 2244 O O2 B BCT D 4 .
O2 1
HETATM 2245 O O3 B BCT D 4 .
O3 1…

? -6.625

1.156

17.4120.33 6.76? 301 CO2 A? -7.570

1.048

16.6760.33 7.80? 301 CO2 A? -5.717

1.284

18.1820.33 7.89? 301 CO2 A? -5.601

0.708

16.6430.67 9.63? 303 BCT A? -6.583

1.348

16.0990.67 12.22? 303 BCT A? -5.469-0.53516.3780.67 9.77? 303 BCT A? -4.819

1.444

17.4420.67 12.28? 303 BCT A

Handling of terminal atoms that should not be included
Terminal atoms (OXT, HXT, H1, H2 and H3 atoms for proteins, OP3, HOP3, HO3 and HO5
atoms for nucleic acids) should not be included for the residues which are not terminal
residues of the sequence, as this does not describe the true content of the crystal and ischemically incorrect. If such atoms are present in the chain, the wwPDB will remove them.
Missing residues (_pdbx_unobs_or_zero_occ_residues, REMARK 465) and atoms(_pdbx_unobs_or_zero_occ_atoms, REMARK 470)
Missing residues (for example: at the N- or C-termini or in flexible loops) and missing side
chain atoms of the polymer component are listed in REMARK 465 if listed in_pdbx_unobs_or_zero_occ_residues with polymer_flag (Y) and occupancy_flag (1).
Similarly, missing atoms are listed in REMARK 470 if listed in_pdbx_unobs_or_zero_occ_atoms with polymer_flag (Y) and occupancy_flag (1). Atoms
which are leaving atoms such as polymer linkage (OXT in amino acids, OP3 in nucleic acids,
O1 in saccharides) and hydrogens will not be listed as missing.
Example:For missing residues
loop__pdbx_unobs_or_zero_occ_residues.id_pdbx_unobs_or_zero_occ_residues.PDB_model_num_pdbx_unobs_or_zero_occ_residues.polymer_flag_pdbx_unobs_or_zero_occ_residues.occupancy_flag_pdbx_unobs_or_zero_occ_residues.auth_asym_id_pdbx_unobs_or_zero_occ_residues.auth_comp_id_pdbx_unobs_or_zero_occ_residues.auth_seq_id_pdbx_unobs_or_zero_occ_residues.PDB_ins_code_pdbx_unobs_or_zero_occ_residues.label_asym_id_pdbx_unobs_or_zero_occ_residues.label_comp_id_pdbx_unobs_or_zero_occ_residues.label_seq_id
1 1 Y 1 A MET 1? A MET 1
2 1 Y 1 A ARG 2? A ARG 2
For missing atoms
loop__pdbx_unobs_or_zero_occ_atoms.id_pdbx_unobs_or_zero_occ_atoms.PDB_model_num_pdbx_unobs_or_zero_occ_atoms.polymer_flag_pdbx_unobs_or_zero_occ_atoms.occupancy_flag_pdbx_unobs_or_zero_occ_atoms.auth_asym_id_pdbx_unobs_or_zero_occ_atoms.auth_comp_id_pdbx_unobs_or_zero_occ_atoms.auth_seq_id_pdbx_unobs_or_zero_occ_atoms.PDB_ins_code_pdbx_unobs_or_zero_occ_atoms.auth_atom_id_pdbx_unobs_or_zero_occ_atoms.label_alt_id_pdbx_unobs_or_zero_occ_atoms.label_asym_id_pdbx_unobs_or_zero_occ_atoms.label_comp_id_pdbx_unobs_or_zero_occ_atoms.label_seq_id_pdbx_unobs_or_zero_occ_atoms.label_atom_id
1 1 Y 1 B ILE 137 ? CG1 ? B ILE 137 CG1
2 1 Y 1 B ILE 137 ? CG2 ? B ILE 137 CG2
3 1 Y 1 B ILE 137 ? CD1 ? B ILE 137 CD1Zero occupancy residues
Some refinement programs allow inclusion of missing residues and side chain atoms in thecoordinate files as atoms with occupancy 0.00. Since these atoms are usually ignored duringrefinement, their location and properties may not be reliable. Therefore, if such atoms areincluded in the deposited coordinate file, these atoms will be retained in the file but also
listed in separate remarks: REMARK 475 if listed in _pdbx_unobs_or_zero_occ_residues
with polymer_flag (Y) and occupancy_flag (0) (for zero occupancy residues) and REMARK
480 if listed in pdbx_unobs_or_zero_occ_atoms with polymer_flag (Y) and occupancy_flag(0). Atoms which are leaving atoms such as polymer linkage (OXT in amino acids, OP3 innucleic acids, O1 in saccharides) and hydrogens will not be listed as missing.
For zero occupancy residues:
loop__pdbx_unobs_or_zero_occ_residues.id_pdbx_unobs_or_zero_occ_residues.PDB_model_num_pdbx_unobs_or_zero_occ_residues.polymer_flag_pdbx_unobs_or_zero_occ_residues.occupancy_flag_pdbx_unobs_or_zero_occ_residues.auth_asym_id_pdbx_unobs_or_zero_occ_residues.auth_comp_id_pdbx_unobs_or_zero_occ_residues.auth_seq_id_pdbx_unobs_or_zero_occ_residues.PDB_ins_code_pdbx_unobs_or_zero_occ_residues.label_asym_id_pdbx_unobs_or_zero_occ_residues.label_comp_id_pdbx_unobs_or_zero_occ_residues.label_seq_id
1 1 Y 0 A PRO 38 ? A PRO 1
2 1 Y 0 A HIS 39 ? A HIS 2

For zero occupancy atoms:
loop__pdbx_unobs_or_zero_occ_atoms.id_pdbx_unobs_or_zero_occ_atoms.PDB_model_num_pdbx_unobs_or_zero_occ_atoms.polymer_flag_pdbx_unobs_or_zero_occ_atoms.occupancy_flag_pdbx_unobs_or_zero_occ_atoms.auth_asym_id_pdbx_unobs_or_zero_occ_atoms.auth_comp_id_pdbx_unobs_or_zero_occ_atoms.auth_seq_id_pdbx_unobs_or_zero_occ_atoms.PDB_ins_code_pdbx_unobs_or_zero_occ_atoms.auth_atom_id_pdbx_unobs_or_zero_occ_atoms.label_alt_id_pdbx_unobs_or_zero_occ_atoms.label_asym_id_pdbx_unobs_or_zero_occ_atoms.label_comp_id_pdbx_unobs_or_zero_occ_atoms.label_seq_id_pdbx_unobs_or_zero_occ_atoms.label_atom_id
1 1 Y 1 A GLN 14 ? CG ? A GLN 16 CG
2 1 Y 1 A GLN 14 ? CD ? A GLN 16 CD
3 1 Y 1 A GLN 14 ? OE1 ? A GLN 16 OE1
4 1 Y 1 A GLN 14 ? NE2 ? A GLN 16 NE2

Ligands or heteroatom groups that are not part of any polymer (protein or nucleic acid) in the
structure may also have missing atoms or atoms with zero occupancy. In such instances thename of the heteroatom group or ligand, chain ID and model number (if applicable) will belisted in _pdbx_unobs_or_zero_occ_atoms with polymer_flag (N) and occupancy_flag (1) orif there are atoms with 0.00 occupancy in pdbx_unobs_or_zero_occ_atoms withpolymer_flag (N) and occupancy_flag (0).

6. Chain ID assignment
Definition of chain ID

The chain ID is a unique identifier for each macromolecular polymer and all chemical groups(including waters) associated with it. The length accepted is up to four characters.
Which moieties are assigned chain IDs?
All atoms in the coordinate section of the PDB entry will be assigned a chain ID.
How will chain IDs be assigned?
Each polymer (amino acid, nucleic acid, or carbohydrate polymer of 2 or more covalently
linked residues) is assigned a unique chain ID. Chain IDs for all bound moieties and waters
are assigned based on their proximity (number of contacts) to the nearest polymer. For
example, all waters and chemical groups around a protein/DNA/RNA polymer are assigned
the chain ID of the polymer they surround. If a polymer chain was cleaved before or during
the experiment, each fragment of the polymer should be assigned a unique chain ID.
Why are chain IDs assigned in this way?
The wwPDB has established this rule to improve the usability and interpretation of thestructural data. Assigning the same chain ID for all moieties associated with a polymer
enables rapid and uniform identification of feature analysis.
How are chain IDs assigned to chemical groups and waters?
All chemical groups and waters within 5 Angstroms of any atom of a polymeric chain will be
associated with that chain and will be assigned the same chain ID as that polymer. If aparticular chemical group/water is equidistant from more than one chain, then the chain ID is
randomly assigned to be that of any one of these polymers. Waters further than 5 Angstroms
away from the polymer that can be moved by symmetry to within 5 Angstroms, will be
automatically moved during entry processing. Waters further than 5 Angstroms away fromany polymer, which cannot be brought closer to a polymer chain by application of symmetry,
will be brought to the attention of the depositor. These waters will be listed in_pdbx_distant_solvent_atoms cif category with the distance to the nearest macromolecule.
loop__pdbx_distant_solvent_atoms.id_pdbx_distant_solvent_atoms.PDB_model_num_pdbx_distant_solvent_atoms.auth_atom_id_pdbx_distant_solvent_atoms.label_alt_id_pdbx_distant_solvent_atoms.auth_asym_id_pdbx_distant_solvent_atoms.auth_comp_id_pdbx_distant_solvent_atoms.auth_seq_id_pdbx_distant_solvent_atoms.PDB_ins_code_pdbx_distant_solvent_atoms.neighbor_macromolecule_distance_pdbx_distant_solvent_atoms.neighbor_ligand_distance
1 1 O ? A HOH 1146 ? 6.79 .
2 1 O ? B HOH 1113 ? 5.96 .

How are chain IDs related to residue numbering?
All residues and chemical groups in a file should be uniquely identified. Once the polymers
and chemical groups associated with them are assigned chain IDs, the numbering of allresidues, chemical groups and waters for each chain ID must be unique. Numbering ofresidues that were not modelled due to limited experimental data should also be consideredhere. The wwPDB encourages deposition of polymer chains with sequential residue
numbering. For protein chains, the authors are encouraged to follow the UniProt residue
numbering, wherever possible. The use of non-sequential residue numbering and insertion

codes should be avoided as much as possible in order to make structures easily interpretableby the larger scientific community. If the coordinate residue numbers, as provided by theauthor, are unique and sequential within a particular chain ID, the residues will not be
renumbered. If the author has already correctly sorted ligands to polymer chains with which
they are associated, these are not reassigned.
How polymer chain IDs should be assigned?
Upper- and lower-case letters, numbers (0-9) and a combination of these should be used forchain IDs. It is preferred that lower case letters and combination of letters/numbers are used
after all upper letters and numbers have been used. Symbols should never be used for chain
IDs.
Consistent use of chain IDs in PDB structures and manuscripts
During the annotation of structures, the numbering and chain IDs of the chemical groups andwaters associated with the polymeric chains may be changed in accordance with the wwPDB
chain ID rules. The wwPDB strongly encourages depositors to use the wwPDB-assigned
chain ID and residue numbers in any publication material. Deposition and processing ofstructures prior to preparation of the manuscript will ensure consistent usage of chain IDs andresidue numbers in the manuscript and the PDB file. Validation and structure analysis reports
generated during annotation may also be helpful in the manuscript preparation.
Structures not compatible with PDB format
Structures that cannot be represented in the legacy PDB file format (PDB incompatible), forexample, structures containing multiple character chain ids, >62 chains, PDB incompatible
secondary structure records and/or >99999 ATOM lines, will be available in the PDB archive
as single PDBx/mmCIF files that represent the entire structure. In addition, these structures
will have TAR files containing a collection of best effort/minimal files in the PDB file format
to support users and software tools that rely solely on the PDB file format. The_pdbx_database_status.pdb_format_compatible flag will be set to N in the mmCIF files forsuch structures:_pdbx_database_status.pdb_format_compatibleN

7. HEADER assignment
How is the header keyword (_struct_keywds.pdbx_keywords) record assigned?
One keyword is used to briefly describe the broad function of the macromolecules present in
the PDB entry. A list of classifications is available at the end of this document and at
ftp://ftp.wwpdb.org/pub/pdb/doc/format_descriptions/class.dat.
Header functions are assigned by the annotator
The annotator typically assigns the function after reviewing the UniProt keywords andkeywords provided by the author. The annotated header will also be included in the entry
keywords (_struct_keywords.text) and if the header is a complex (/ separated), the word‘complex’ will be added in the keywords. If protein is an enzyme, the general class of
enzymes is used. For example, the header is assigned as oxidoreductase if the E.C. number
starts with 1. See Appendix A or
ftp://ftp.wwpdb.org/pub/pdb/doc/format_descriptions/class.dat for the list of available
headers.
• If protein has no known function, "UNKNOWN FUNCTION" is used.

•••

If the function is putative, such as a "putative hydrolase" the header will be assigned
based on the putative assignment, i.e., "HYDROLASE".
If the annotator is unsure of the function, the annotator asks the author to choose theappropriate header from within the standard header list.
If the function is new to the PDB, a generalized header describing the function will be
added to the standard header list.

Two or more HEADERs can be combined using the following rules:• For macromolecular complexes, the headers are separated with a forward slash(HEADER1/HEADER2). e.g., TRANSCRIPTION/DNA (Note that protein is listed
first in protein/nucleic acid complexes).
• The word "complex" will not be used in the header record but will appear in the
keywords record whenever there is a "/" in the header.
• A multifunctional macromolecule will have commas between the different headers:
HEADER1,HEADER2• Functions such as inhibitor, activator, receptor, substrate of a macromolecule can be
added to existing headers (HEADER INHIBITOR) e.g., HYDROLASE INHIBITOR,HYDROLASE ACTIVATOR, HYDROLASE RECEPTOR, HYDROLASEREGULATOR.
How are keywords (_struct_keywords.text) assigned?
Keywords are provided by the entry author. The header keyword (from_struct_keywds.pdbx_keywords) record will also be listed here.

8. Assembly
Quaternary assembly (_pdbx_struct_assembly, _pdbx_struct_assembly_gen,_pdbx_struct_oper_list)
The quaternary structure in a PDB entry may include software calculated quaternary
assembly and/or author determined biological assembly, or the biologically relevant form of
the molecule for which there is experimental evidence.
We derive a likely oligomeric state of the structure based on the surface area of interactions
and the association of macromolecules. Frequently, this derived structure and the biologicalassembly are the same. However, due to crystal packing forces, experimental evidence, or
author opinion, the biological assembly and the derived oligomeric structure may bedifferent. For example, a macromolecule may be assigned a hexameric quaternary structure in
the crystal, but the biological assembly may be monomeric. It is recognized that quaternary
structure programs such as PISA1 and PQS2 do not work with every case, such as antibodies,or any case where a biological process has a low association/dissociation property. The
quaternary assembly is calculated and evaluated by the annotation staff, in addition to the
biological assembly information provided by the author, known from the literature or similar
structures in the PDB archive.
The matrices forming the quaternary structure will be reported in _pdbx_struct_oper_list
mmCIF category and will be assigned by the wwPDB annotators. In instances where theauthor's description of the biological assembly disagrees with what the crystal structureappears to present, the biological assembly can be chosen by the depositor, and reported in
the file. The total surface area, buried surface area and free energy gain will be listed if twopolymers have an interface.

Nomenclature: The number of subunits in an oligomeric complex are described using namesthat end in -mer (Greek for "part, subunit"). Formal Greco-Latinate names are generally used
for the first ten types and can be used for up to twenty subunits, whereas higher ordercomplexes are usually described by the number of subunits, followed by -meric.
In pdbx_struct_assembly.oligomeric_details and pdbx_struct_assembly.oligomeric_count,any polypeptide of length of 3 or more amino acids or 2 or more nucleotides is considered in
the naming of a quaternary structure as monomeric or dimeric etc.:
1 = monomeric
8 = octameric
15 = pentadecameric
2 = dimeric
9 = nonameric
16 = hexadecameric
3 = trimeric
10 = decameric
17 = heptadecameric
4 = tetrameric
11 = undecameric
18 = octadecameric
5 = pentameric
12 = dodecameric
19 = nonadecameric
6 = hexameric
13 = tridecameric
20 = eicosameric
7 = heptameric
14 = tetradecameric
21-meric etc.
Please note that the multi-mer described in PDB remark 350 represents either homo or hetero
multi-mer for that entry.

9. Miscellaneous records
File versioning and revision history
The wwPDB maintains a file versioning system that allows Depositors of Record to update
their own previously released entries.
Version numbers of each PDB archive entry is designated using a #-# identifier. The first
digit specifies the major version, and the second designates the minor version. The Structureof Record (i.e., the initial set of released atomic coordinates) is designated as Version 1-0.
Thereafter, the major version digit is incremented with each substantial revision of a given
entry (e.g., Version 2-0, when the atomic coordinates are replaced for the first time by the
Depositor of Record). “Major version changes” are defined as updates to the atomic
coordinates, polymer sequence(s), and/or chemical identify of a ligand. All other changes aredefined as “minor changes”. When a major change is made, the minor version number is reset
to 0 (e.g., 1-0 to 1-1 to 2-0). The wwPDB retains all major versions with the latest minor
versions of an entry within the PDB archive.
Special audit categories are used to capture details of changes to files down to the category
level for entry revisions:
http://mmcif.wwpdb.org/dictionaries/mmcif_pdbx_v50.dic/Groups/audit_group.html
For example:
loop__pdbx_audit_revision_history.ordinal_pdbx_audit_revision_history.data_content_type_pdbx_audit_revision_history.major_revision_pdbx_audit_revision_history.minor_revision_pdbx_audit_revision_history.revision_date
1 'Structure model' 1 0 2020-03-25
2 'Structure model' 1 1 2020-04-08
3 'Structure model' 1 2 2020-05-06#_pdbx_audit_revision_details.ordinal1

_pdbx_audit_revision_details.revision_ordinal1_pdbx_audit_revision_details.data_content_type'Structure model'_pdbx_audit_revision_details.provider
repository_pdbx_audit_revision_details.type'Initial release'_pdbx_audit_revision_details.description?
_pdbx_audit_revision_details.details
?
#
loop_
_pdbx_audit_revision_group.ordinal_pdbx_audit_revision_group.revision_ordinal_pdbx_audit_revision_group.data_content_type_pdbx_audit_revision_group.group
1 2 'Structure model' 'Database references'
2 2 'Structure model' 'Structure summary'
3 3 'Structure model' 'Database references'
4 3 'Structure model' 'Source and taxonomy'
5 3 'Structure model' 'Structure summary'#loop__pdbx_audit_revision_category.ordinal_pdbx_audit_revision_category.revision_ordinal_pdbx_audit_revision_category.data_content_type_pdbx_audit_revision_category.category
1 2 'Structure model' entity
2 2 'Structure model' pdbx_related_exp_data_set
3 3 'Structure model' entity
4 3 'Structure model' entity_name_com
5 3 'Structure model' entity_src_gen
6 3 'Structure model' struct_ref
7 3 'Structure model' struct_ref_seq#
loop__pdbx_audit_revision_item.ordinal_pdbx_audit_revision_item.revision_ordinal_pdbx_audit_revision_item.data_content_type_pdbx_audit_revision_item.item
1 2 'Structure model' '_entity.pdbx_description'
2 3 'Structure model' '_entity.pdbx_description'
3 3 'Structure model' '_entity.pdbx_ec'
4 3 'Structure model' '_entity_src_gen.gene_src_common_name'
5 3 'Structure model' '_entity_src_gen.pdbx_gene_src_gene'
6 3 'Structure model' '_struct_ref.db_code'
7 3 'Structure model' '_struct_ref.db_name'
8 3 'Structure model' '_struct_ref.pdbx_align_begin'
9 3 'Structure model' '_struct_ref.pdbx_db_accession'
10 3 'Structure model' '_struct_ref.pdbx_seq_one_letter_code'
11 3 'Structure model' '_struct_ref_seq.db_align_beg'
12 3 'Structure model' '_struct_ref_seq.db_align_end'
13 3 'Structure model' '_struct_ref_seq.pdbx_db_accession'

Link records (_struct_conn, LINK, SSBOND)
LINK records will be automatically generated using standard software. There are various
cutoff distances specified in this software for various kinds of LINK records. LINK records
can include covalent bonding, metal coordination etc. LINK records may also be added by
the author.

SSBOND records are created for cysteine residues involved in disulfide bonds and do notinclude disulfide bonds between other residues or ligands.
Standard software will automatically add the struct_conn category to the file, listing the
distances of the link records between metal ions and surrounding residues following standard
coordination geometry. Below is an excerpt of LINK records in PDB entry 1W3M.
mmCIF format:
loop__struct_conn.id_struct_conn.conn_type_id_struct_conn.pdbx_leaving_atom_flag_struct_conn.pdbx_PDB_id_struct_conn.ptnr1_label_asym_id_struct_conn.ptnr1_label_comp_id_struct_conn.ptnr1_label_seq_id_struct_conn.ptnr1_label_atom_id_struct_conn.pdbx_ptnr1_label_alt_id_struct_conn.pdbx_ptnr1_PDB_ins_code_struct_conn.pdbx_ptnr1_standard_comp_id_struct_conn.ptnr1_symmetry_struct_conn.ptnr2_label_asym_id_struct_conn.ptnr2_label_comp_id_struct_conn.ptnr2_label_seq_id_struct_conn.ptnr2_label_atom_id_struct_conn.pdbx_ptnr2_label_alt_id_struct_conn.pdbx_ptnr2_PDB_ins_code_struct_conn.ptnr1_auth_asym_id_struct_conn.ptnr1_auth_comp_id_struct_conn.ptnr1_auth_seq_id_struct_conn.ptnr2_auth_asym_id_struct_conn.ptnr2_auth_comp_id_struct_conn.ptnr2_auth_seq_id_struct_conn.ptnr2_symmetry_struct_conn.pdbx_ptnr3_label_atom_id_struct_conn.pdbx_ptnr3_label_seq_id_struct_conn.pdbx_ptnr3_label_comp_id_struct_conn.pdbx_ptnr3_label_asym_id_struct_conn.pdbx_ptnr3_label_alt_id_struct_conn.pdbx_ptnr3_PDB_ins_code_struct_conn.details_struct_conn.pdbx_dist_value_struct_conn.pdbx_value_ordercovale1
covale both ? M LNG . C1 A ? ? 1_555 A
A ASP 1
1_555 ? ? ? ? ? ? ? 1.306 ?
covale2
covale both ? M LNG . C1 B ? ? 1_555 A
A ASP 1
1_555 ? ? ? ? ? ? ? 1.350 ?
covale3
covale one ? A ASP 1 C? ? ? 1_555 A
A VLL 2
1_555 ? ? ? ? ? ? ? 1.334 ?
covale4
covale both ? A VLL 2 C? ? ? 1_555 A
A CPI 3
1_555 ? ? ? ? ? ? ? 1.340 ?
metalc1
metalc ?
? A VLL 2 O? ? ? 1_555 N
A CA 3013 1_555 ? ? ? ? ? ? ? 2.335 ?
covale5
covale one ? A VLL 2 NG2 ? ? ? 1_555 A

ASP 1

N

? ? A LNG 0

ASP 1

N

? ? A LNG 0

VLL 2

N

? ? A ASP 1

CPI 3

N

? ? A VLL 2CACA? ? A VLL 2

PRO 11 C? ? A VLL 2.

Secondary structure records
Helix and sheet records are automatically generated by the Promotif algorithm, and stored in
the struct_conf, struct_sheet, struct_sheet_order, struct_sheet_range andpdbx_struct_sheet_hbond categories. Authors who wish to provide their own helix and sheetrecords may do so.

From June 2021, PDB formatted files are no longer generated for PDB entries where thesheet topology cannot be generated in the PDB format (complex beta sheet topologies where
the definition of the strands within a beta sheet cannot be presented in a linear description).
This limitation, however, is not an issue in the PDBx/mmCIF formatted file, where thesecomplex beta sheet topologies can be correctly captured. Therefore, for these examples,
wwPDB will continue to provide secondary structure with helix and sheet information in the
PDBx/mmCIF formatted file.
Validation, calculation of bond, angle, torsion deviations, etc.
The calculation of bond and angle deviations for protein entries will be based on the updated
Engh & Huber amino acid target values3. For nucleic acids, the Parkinson et al., statistics areused for these calculations4. All bonds and angles that deviate more than 6 times from theirstandard target values will be flagged as a deviation. The PHI/PSI values are based on
Kleywegt’s calculations5.
The deviations are reported in mmcif categories below, and REMARK 500 of PDB format
file.
CLOSE CONTACTS IN SAME ASYMMETRIC UNIT (_pdbx_validate_close_contact)
SYMMETRY RELATED CLOSE CONTACTS (_pdbx_validate_symm_contact)
BOND LENGTHS (_pdbx_validate_rmsd_bond)
BOND ANGLES (_pdbx_validate_rmsd_angle)
TORSION ANGLES (_pdbx_validate_torsion)
NON-CIS, NON-TRANS (_pdbx_validate_peptide_omega)
SIDE CHAIN PLANAR GROUPS (_pdbx_validate_planes)
MAIN CHAIN PLANARITY (protein only) (_pdbx_validate_main_chain_plane)
CHIRAL CENTERS (protein C-alpha only) (_pdbx_validate_chiral)
Additional entry details
Additional entry details are annotated in _pdbx_entry_details, such as additional functional
details of the compounds in _pdbx_entry_details.compound_details (REMARK 400),
additional polymer sequence details in _pdbx_entry_details.sequence_details (REMARK999), and any other information about the ligand in _pdbx_entry_details.nonpolymer_details(REMARK 600).
Related entries
Authors may provide information about related entries (pdbx_database_related, REMARK900) to relate other entries to the current entry.
Deprecation of _struct_site (SITE) records
In June 2021 the in-house legacy software which produced _struct_site and _struct_site_gen
records was retired. At that point, the wwPDB no longer generated these categories for newly
deposited PDB entries, however existing entries were unaffected.

10. Structural Genomics Entries
Structural genomics (SG) entries are usually either X-ray or NMR structures deposited by thevarious structural genomics groups around the world. In the USA, these structures aredeposited primarily by the several Protein Structure Initiative (PSI) groups. Europe, UK,

Canada and Japan also have several structural genomics centers. The SG structures areprocessed in the same way as any other PDB deposition. There are just a few additional rules
for the annotation of these entries. These are listed below:• Usually, the SG entries are deposited with a "release immediately" status. In special
instances (like for the CASP competition) the depositions may be processed and held
for a pre-determined period before its release.
• For entries deposited by an SG group, the author list also includes the name of the SG
center (like JCSG, MCSG, BSGC, etc.).
• The following words and phrases are also included in the keywords: SG center name(in full and also the abbreviation), Structural Genomics. If the entry is from a PSI
center, the initials "PSI" and the words "Protein Structure Initiative" are added to the
keywords. Entries that are part of the second phase of the PSI project are labelled PSI2.
• For SG entries deposited by centers which also deposit targets to TargetDB, theTargetDB ID for each sequence in the entry is included in the file and it appears in_pdbx_database_related (REMARK 900).
• The project name, center name and center abbreviation are included in the_pdbx_SG_project mmCIF category.

11. Information specific to X-ray structures
Deposition of X-ray structures
All structures determined by crystal X-ray diffraction where the structure is that of a nonvirus capsid should contain the atomic coordinates for the whole crystallographic asymmetricunit (ASU). The ASU is defined as the smallest unit that can be rotated and translated togenerate one unit cell using only the symmetry operators allowed by the crystallographic
symmetry. The asymmetric unit may be one molecule or one subunit of a multimeric protein,but it can also be more than one.
Information contained in structure factor files
Structure factor (sf) files should include information such as cell, space group, symmetry,wavelength, and number of reflections of the entry. The date included in the header of the sf
file will be the date of release, not the deposition date. If authors include multiple structure
factor files (such as a set for refinement, multiple sets for phasing, etc.), the data will bearchived as multiple data blocks. For example, the reflections for refinement will be listed in
the category '_refln' and the phasing data sets will be listed in the category'_phasing_set_refln.' The different data sets can be distinguished by crystal and/or
wavelength ID as appropriate. If different cell dimensions are present, this information will
also be included in the file. The dataset used for the refinement should be listed as a first data
block and should contain diffraction indices h,k,l, observed amplitudes and/or intensities,
their respective sigma values and refinement test set.
See Appendix B for examples of the structure factor files.
Refinement and data collection statistics significant figures
The values provided by the author will be retained in the mmCIF and PDB files.
Hydrogens in crystal structures
Hydrogens in crystal structures will be retained regardless of resolution with the occupancy
provided by the depositor.

Matthews coefficient and solvent content
For crystal structures, the Matthews coefficient and solvent content will be automaticallycalculated using the following equations:
Matthews coefficient6 = volume of unit cell/(the molecular weight of macromolecule*Y*X)
Where Y is the number of asymmetric units in the unit cell (i.e., the number of symmetry
operators in the space group). The unknown variable, X, is the number of molecules in theasymmetric unit.
Solvent content = 1 - 1.23/ (Matthews coefficient)
The molecular weight includes protein and nucleic acids based on sequences, no water andligands. In cases of viral capsids and proteolytic fragments, the Matthews coefficient andsolvent content should be author provided and will not be automatically calculated.
Number of reflections
The number of reflections for refinement is the number of crystallographically uniquemeasured reflections that satisfy both the resolution and the observation limits. The numberof reflections for data collection is the total number of crystallographically unique measured
reflections that are labelled as observed by the criterion on sigma(I) or on sigma(F). The
number of reflections reported for refinement should be less than or equal to the number
reported for data collection, even if Friedel pairs were used.
Twinned structures
Structures based on twinned crystal diffraction data can be identified through use of thetwinning tokens to the mmCIF public exchange dictionary, pdbx_twin. The tokens can beused for identification of twinning operator, type, and fraction.
The structure factor file for a twinned structure should include the twinned data used forrefinement first. If the authors have the detwinned data, it may also be included in the file.
The pdbx_reflns_twin tokens should be included in the structure factor file.
MAD data
If MAD data were collected, authors are encouraged to provide all data sets used in structure
solution and refinement. The data set used for refinement should be listed first in the structure
factor file. Authors are encouraged to provide the other (phasing) datasets. Wavelengths,
source and other data collection information for all data sets should also be provided.
BioSync and information about synchrotron data collection
Information about synchrotron sources and beamlines will be made consistent with thestandard names used in the BioSync database (http://biosync.rcsb.org/).

12. Information specific to NMR structures
Pseudoatoms (Q atoms)
Pseudoatoms (also known as Q atoms) submitted for NMR entries will be removed from theentry.
Superimposed models
At least one domain of the NMR entry should be superimposed across all models. It is
recognized that for multi-domain NMR structures, domain movements prevent the whole
structure from being aligned through the length of the molecule. However, in order tohighlight the relative movement of the domains, it makes sense to superpose at least one partof the structure across all the models deposited under a PDB accession code. This does notdetract from the scientific value of the coordinate set or the experiment, but on the contrary,
serves to highlight domain motion with respect to a fixed point. The superposition need not
be arbitrary but may be done at the choosing of the depositor. This will allow the larger
scientific community easy identification of the protein folds. It also facilitates identificationof model variations across different parts of the structure.
Experimental Methods: There are two types of NMR experimental methods (EXPDTA,_exptl.method):
SOLID-STATE NMR
SOLUTION NMR
Homogeneity of Ensemble
All models in a deposition should be superimposed in an appropriate author determinedmanner and only one superposition method should be used. Structures from different
experiments, or different domains of a structure, should not be superimposed and deposited
as models of a deposition.
All models in an NMR ensemble must be homogeneous - each model must have the exact
same atoms (hydrogen and heavy atoms), sequence and chemistry.
Deposition of minimized average structure must be accompanied with ensemble and must be
homogeneous with ensemble.
Model type
MDLTYP record contains additional annotation pertinent to the coordinates presented in theentry. This record will indicate minimized average structure with model number of theminimized average structure. The corresponding cif is _struct.pdbx_model_type_details.
MDLTYP MINIMIZED AVERAGE, MODEL X
Best representative conformer
This record defines the best representative conformer in the ensemble(pdbx_nmr_representative.conformer_id, REMARK 210).
Example:_pdbx_nmr_representative.conformer_id_pdbx_nmr_representative.selection_criteria

1"lowest energy"

During the annotation of structures, the best representative conformer is moved to MODEL 1
since HELIX/SHEET, SITE and LINK records are generated based on the first model in thecoordinates. Authors are notified of how the annotation staff handled this case.

13. Information specific to Electron Microscopy structures
There are two types of general experimental methods for 3DEM: electron microscopy (EM;comprises single particle and helical reconstruction techniques, tomography, andsubtomogram averaging) and electron crystallography (EC). There are three main data filetypes associated with 3DEM:• 3D volume, or map• Atomic coordinates• Structure factors (EC only)An EM deposition may comprise map only, coordinates and map, or only coordinates. Any
atomic coordinates deposited must have an associated map, i.e., the map from which thosecoordinates were derived. That associated map must be the either the primary (see Map
Information section below) map of the shared deposition (in the case of a deposition
containing both map and coordinates) or the primary map of a different deposition. In any
case, the EMDB ID of the map must be included in _pdbx_database_related (REMARK 900)
as “associated EM volume” (any other related maps will be designated as “other EM
volume”). In addition, no EM atomic coordinates will be released to the PDB without
simultaneous or previous release of its associated map to the EMDB.
An EC deposition will generally comprise only coordinates and structure factors, analogous
to X-ray crystallography. Occasionally, a map will also be included in the deposition or
associated from a different deposition. In the absence of structure factors, there must be an
associated map. Maps for EC depositions must be treated identically to maps for EM
depositions.
In addition to the three main data file types, there are some auxiliary file types:• Map image file (mandatory for depositions that include maps)• FSC curve XML (optional; should be the FSC curve used to estimate the reported
resolution)• Layer lines (optional for tomography entries)
Map Information
Maps are accepted in two formats, CCP4 and MRC, and will be converted to CCP4 format
upon deposition. There are three depositor-provided data items associated with each map:the voxel size (in pixels / Angstrom; mandatory for all maps), the recommended contour level(for optimal display of isocontour maps; mandatory for all maps except tomograms), andannotation details (a brief description of the map; optional for all maps). There are four
different subtypes assigned to maps:• Primary map. The primary map is the center of a map deposition (and EMDB
entry). If maps are deposited, a primary map is mandatory. Each deposition will have
only one primary map, and map validation presented by the wwPDB will be focusedon the primary map. If deposited coordinates are derived from a map, that map must
be a primary map.
• Half map. Half maps are the two maps (based on alternate halves of the data set)
used for cross-validation during reconstruction of the primary map. Deposition ofhalf maps is optional but encouraged. If half maps are provided, there must be two
and only two, and they should be unaltered and uncropped.
• Mask. Masks are used during map processing for removing noise, improving map
quality, isolating portions of maps (segmenting), etc. Deposition of masks is optional,
and any number of masks can be included as part of a deposition.
• Additional map. Any maps included in a deposition that are not the primary map,the half maps associated with the primary map, or masks are labeled “additionalmaps”. These can include raw maps, unmasked maps, segmentations, etc. Depositionof additional maps is optional, and any number of additional maps can be included aspart of a deposition.
EM Metadata
Additional metadata are collected for 3DEM depositions relative to other PDB depositions.
Generally, these involve the equipment and parameters related to 3DEM data collection and3D volume reconstruction, as well as refinement of atomic coordinates where relevant. In
PDBx/mmCIF, these metadata are designated _em_* (where * is a wildcard). They

correspond to metadata collected for use by EMDB, though some but not all of the metadata
will be also be used by the PDB.

14. Viral capsids and other complex assemblies
For the purposes of annotation, a complex assembly is defined as a structure for which thefull biological assembly and/or crystallographic asymmetric unit is built by applying a set of
non-crystallographic rotation/translation transformations to a set of deposited coordinates.
Icosahedral Viruses
The icosahedral virus is the most common complex assembly deposited to the PDB. The
author generally deposits the coordinates of the icosahedral asymmetric unit and supplies aset of 60 transformation matrices to be applied to the coordinates to produce the fullbiological assembly. We will continue to request these matrices from the authors. From theauthor-provided matrices and coordinates we will calculate a standard set of 60 orderedmatrices as well as the transformation that moves the complex to the standard icosahedral
frame (same frame used by ViperDB). The calculated matrices, the frame transformation, andthe description of how they are to be applied to the coordinates to build the assembly will be
stored in _pdbx_struct records.
For crystal structures we will also request a complete description of how to build the crystal
asymmetric unit, and the description will be archived in _pdbx_struct records. If thecoordinates are provided in the crystal frame, the non-crystallographic symmetrytransformations will also be placed in struct_ncs_oper records and will appear in MTRIX
records, enabling validation against the structure factor data.
Regular Symmetries
Icosahedral point symmetry is just one type of symmetry that can be adopted by a complex
assembly. Other point symmetries (see table below) or helical symmetries are possible. For
all structures deposited as complex assemblies, we will archive symmetry information as
appropriate in _pdbx_point_symmetry or _pdbx_helical_symmetry records.
point
Schoenflies# equivalent
symmetry
symbolpositionscircularCnndihedralDn
2ntetrahedralT12octahedralO
24
icosahedral
I
60
From: International Tables for Crystallography, Volume A, 4th edition, Table 10.4.2, p. 782783
Point symmetry
The point symmetry information is stored in the pdbx_point_symmetry category (REMARK300).
Example:_pdbx_point_symmetry.entry_id 2BK1
_pdbx_point_symmetry.Schoenflies_symbol C_pdbx_point_symmetry.circular_symmetry 38

T = TETRAHEDRAL
D = DIHEDRALO = OCTAHEDRALI = ICOSAHEDRAL

15. Re-refinement of another author's data
The following text is for a dedicated remark for cases where an author re-refines anotherauthor's data (pdbx_database_remark, REMARK 0). The remark will always appear in entries
where the author refined someone else's data. The entry will be treated as an experimental
structure.
Example of the entry 1ZET, based on the data of 1T3N:_pdbx_database_remark.id0_pdbx_database_remark.text;THIS ENTRY 1ZET REFLECTS AN ALTERNATIVE MODELING OF THESTRUCTURAL DATA IN
R1T3NSF ORIGINAL DATA DETERMINED BYAUTHOR:
D.T.NAIR,R.E.JOHNSON,S.PRAKASH,L.PRAKASH,A.K.AGGARWAL;#

Original author's paper in will be listed in citation category with citation_id =original_data_1:
loop__citation.id_citation.title_citation.journal_abbrev_citation.journal_volume_citation.page_first_citation.page_last_citation.year_citation.journal_id_ASTM_citation.country_citation.journal_id_ISSN_citation.journal_id_CSD_citation.book_publisher_citation.pdbx_database_id_PubMed_citation.pdbx_database_id_DOI
primary 'DNA polymerases: Hoogsteen base-pairing in DNA replication?'
Nature 437 E6 '7; discussion E7' 2005 NATUAS UK 0028-0836 0006 ? 16163299
10.1038/nature04199
original_data_1 'Replication by human DNA polymerase-iota occurs by
Hoogsteen base-pairing.' Nature 430 377 380
2004 NATUAS UK
0028-0836 0006 ? 15254543 10.1038/nature02692#
loop__citation_author.citation_id_citation_author.name_citation_author.ordinal
primary'Wang, J.'
1
original_data_1 'Nair, D.T.'
2
original_data_1 'Johnson, R.E.' 3
original_data_1 'Prakash, S.'
4original_data_1 'Prakash, L.'5
original_data_1 'Aggarwal, A.K.' 6

Note: In entries where pdbx_database_remark (REMARK 0) is included as described above,
pdbx_database_related (REMARK 900) will also reflect the reuse of existing experimental
data as shown in the example below:#_pdbx_database_related.db_namePDB_pdbx_database_related.db_id
1T3N_pdbx_database_related.details'Structure of the catalytic core of
DNA polymerase Iota in complex with DNA and dTTP'_pdbx_database_related.content_type
re-refinement

The SF file has the following, with additional information on what the author added, if
applicable:_audit.revision_id
1_0_audit.creation_date 2005-07-19_audit.update_record;Initial release, author used sf file from pdb entry 1t3n, and added
columns Fcalc, phases and FOM;

Appendices:
A. HEADER list (struct_keywords.pdbx_keywords)
Below is the list of headers to be used when processing PDB entries:
ALLERGENANTIBIOTIC (peptidic, saccharide containing)
ANTIFREEZE PROTEIN
ANTIFUNGAL PROTEIN
ANTIMICROBIAL PROTEIN
ANTITOXINANTITUMOR PROTEINANTIVIRAL PROTEINAPOPTOSISATTRACTANT
BIOSYNTHETIC PROTEINBLOOD CLOTTINGCARBOHYDRATE
CELL ADHESIONCELL CYCLECELL INVASION
CHAPERONECIRCADIAN CLOCK PROTEINCONTRACTILE PROTEINCYTOKINE (includes interleukins, interferons)
DE NOVO PROTEIN (ARTIFICIALLY DESIGNED, OFTEN SYNTHETIC)DNA
DNA-RNA HYBRID (used when biological assembly contains mixed DNA and RNA
residues or strands)

ELECTRON TRANSPORTENDOCYTOSISEXOCYTOSISFLAVOPROTEINFLUORESCENT PROTEIN
GENE REGULATION (use only when TRANSCRIPTION, REPLICATION,
TRANSLATION are not applicable)
HORMONE
HYDROLASE (E.C.3.-.-.-)IMMUNE SYSTEM (includes antibodies, antigens)
IMMUNOSUPPRESSANT
ISOMERASE (E.C.5.-.-.-)LIGASE (E.C.6.-.-.-)
LIPID TRANSPORTLUMINESCENT PROTEINLYASE (E.C.4.-.-.-)MEMBRANE PROTEIN (no other function known)
METAL TRANSPORTMOTOR PROTEINNEUROPEPTIDEONCOPROTEINOXIDOREDUCTASE (E.C.1.-.-.-)OXYGEN BINDING
OXYGEN STORAGEOXYGEN TRANSPORTPHOTOSYNTHESISPLANT PROTEIN (no other function known)
PROTON TRANSPORTPROTEIN TRANSPORT (a protein involved in transporting other protein)
RECOMBINATIONREPLICATIONRIBOSOME (use only when TRANSLATION is not correct; do not specify /RNA evenwhen present!)
RIBOSOMAL PROTEINRNASIGNALING PROTEIN (includes G-proteins)
SPLICING
STRUCTURAL GENOMICS (product of a probable gene)
STRUCTURAL PROTEIN
SURFACTANT PROTEIN
TOXIN (not antibiotic, can use e.g. HYDROLASE INHIBITOR, TOXIN)
TRANSFERASE (E.C.2.-.-.-)
TRANSCRIPTION (DNA to RNA)TRANSLATION (protein synthesis; prefer over RIBOSOME)
TRANSLOCASE (E.C.7.-.-.-)
TRANSPORT PROTEIN (a protein that transports anything)
NUCLEAR PROTEIN (whether involved in binding RNA/DNA or some sort of nuclear
processing is unclear)
VIRUS (for entire viral capsid)
VIRAL PROTEIN (viral protein not involved in the viral capsid)

VIRUS LIKE PARTICLE ((for cases where virus like particles are assembled , but are not
the standard virus)
When no other function is known use the following:
CHOLINE-BINDING PROTEINCYTOSOLIC PROTEIN (a protein whose function is not known well but is known to befound in the cytosol of a cell.)DNA BINDING PROTEIN
RNA BINDING PROTEIN
LIPID BINDING PROTEINMETAL BINDING PROTEIN (such as ZN, FE)
PEPTIDE BINDING PROTEIN
PROTEIN BINDING (implies binding of protein by protein)
SUGAR BINDING PROTEIN
xxx-BINDING PROTEIN (for any xxx ligand if none of above applies, such as HEME,AVIDIN, BIOTIN)PROTEIN FIBRILUNKNOWN FUNCTION

B. Format for Structure Factors
Example 1 Structure factor file containing single data set used for refinement
data_rxxxxsf#_audit.revision_id
1_0_audit.creation_date?
_audit.update_record'Initial release'##_entry.id
xxxx##_cell.entry_id
xxxx_cell.length_a118.8600_cell.length_b155.0300_cell.length_c155.5400_cell.angle_alpha90.0000_cell.angle_beta
90.0000_cell.angle_gamma
90.0000#_symmetry.entry_id
xxxx_symmetry.Int_Tables_number
20_symmetry.space_group_name_H-M'C 2 2 21'#
loop__symmetry_equiv.id_symmetry_equiv.pos_as_xyz
1 'X, Y, Z'
2 '-X, -Y, Z+1/2'
3 'X, -Y, -Z'
4 '-X, Y, -Z+1/2'
5 'X+1/2, Y+1/2, Z'
6 '-X+1/2, -Y+1/2, Z+1/2'
7 'X+1/2, -Y+1/2, -Z'
8 '-X+1/2, Y+1/2, -Z+1/2'##

_diffrn.id
1_diffrn.crystal_id1_diffrn.details?
#_diffrn_radiation_wavelength.id1_diffrn_radiation_wavelength.wavelength
0.98100#_exptl_crystal.id1#_reflns_scale.group_code
1
#
loop_
_refln.wavelength_id_refln.crystal_id_refln.scale_group_code_refln.index_h_refln.index_k_refln.index_l_refln.status_refln.F_meas_au_refln.F_meas_sigma_au_refln.F_calc_refln.phase_calc_refln.fom_refln.pdbx_HL_A_iso_refln.pdbx_HL_B_iso_refln.pdbx_HL_C_iso_refln.pdbx_HL_D_iso
1 1 1
0
0
6 o
299.0
6.4
1306.2
0.0
0
0.00
0.00
1 1 1
0
0
10 o
726.8
15.0
1756.7
180.0
0.00
0.00
...
#END OF REFLECTIONS

0.32

0.33

0.99

2.86

0

Example 2 Structure factor file containing data sets for final refinement and phasing
data_rxxxxsf#_audit.revision_id
1_0_audit.creation_date?
_audit.update_record'Initial release'##This file contains two data sets. The first data set is used forrefinement.
#The second data set is used for phasing.
#_entry.id
xxxx##_cell.entry_id
xxxx_cell.length_a108.7420_cell.length_b61.6790_cell.length_c71.6520_cell.angle_alpha90.0000_cell.angle_beta
97.1510_cell.angle_gamma
90.0000#_symmetry.entry_id
xxxx_symmetry.Int_Tables_number
5_symmetry.space_group_name_H-M'C 1 2 1'#

loop__symmetry_equiv.id_symmetry_equiv.pos_as_xyz
1 'X, Y, Z'
2 '-X, Y, -Z'
3 'X+1/2, Y+1/2, Z'
4 '-X+1/2, Y+1/2, -Z'##_diffrn.id
1_diffrn.crystal_id1_diffrn.details“data used for final refinement”#_diffrn_radiation_wavelength.id1_diffrn_radiation_wavelength.wavelength
1.0#_exptl_crystal.id1#_reflns_scale.group_code
1
#
loop_
_refln.wavelength_id_refln.crystal_id_refln.scale_group_code_refln.index_h_refln.index_k_refln.index_l_refln.status_refln.F_meas_au_refln.F_meas_sigma_au
1 1 1
-50
0
1 x
?
?
1 1 1
49
5
1 o
37.7
9.4
1 1 1
50
0
0 x
?
?
...
#END
data_rxxxxAsf##This is second data set for phasing.
###_cell.entry_id
xxxx_cell.CCP4_wavelength_id1_cell.CCP4_crystal_id1_cell.length_a108.742_cell.length_b61.689_cell.length_c71.652_cell.angle_alpha90.000_cell.angle_beta
91.151_cell.angle_gamma
90.000#_symmetry.entry_id
xxxx_symmetry.Int_Tables_number
5_symmetry.space_group_name_H-M'C 1 2 1'#loop__symmetry_equiv.id_symmetry_equiv.pos_as_xyz
1 'X, Y, Z'
2 '-X, Y, -Z'

3 'X+1/2, Y+1/2, Z'
4 '-X+1/2, Y+1/2, -Z'##_diffrn.id
1_diffrn.crystal_id1_diffrn.details“data used for phasing”#_diffrn_radiation_wavelength.id 1_diffrn_radiation_wavelength.wavelength
0.98100#_entry.id xxxx#
_exptl_crystal.id 1#_reflns_scale.group_code
1
#
loop_
_refln.wavelength_id_refln.crystal_id_refln.scale_group_code_refln.index_h_refln.index_k_refln.index_l_refln.status_refln.F_meas_au_refln.F_meas_sigma_au_refln.pdbx_anom_difference_refln.pdbx_anom_difference_sigma
1 1 1
-50
0
1 x
?
1 1 1
-50
0
2 x
?
...
#END OF REFLECTIONS

?
?

?
?

?
?

Example 3 Structure factor file containing data sets for final refinement and scaled
unmerged intensities
data_rxxxxsf#
loop__audit.revision_id_audit.creation_date_audit.update_record
1_0 2009-12-08 'Initial release'
1_1 2016-08-10 'unmerged data added'#_cell.entry_id
xxxx_cell.length_a44.0630_cell.length_b75.9360_cell.length_c85.9440_cell.angle_alpha90.0000_cell.angle_beta
90.0000_cell.angle_gamma
90.0000#_diffrn.id
1_diffrn.crystal_id1_diffrn.ambient_temp?
_diffrn.crystal_treatment?
_diffrn.details'amplitudes used for refinement'#

_diffrn_radiation_wavelength.id1_diffrn_radiation_wavelength.wavelength
1.5418#_diffrn_reflns.diffrn_id1_diffrn_reflns.pdbx_d_res_high
1.769_diffrn_reflns.pdbx_d_res_low
19.546_diffrn_reflns.limit_h_max
24_diffrn_reflns.limit_h_min0_diffrn_reflns.limit_k_max
42_diffrn_reflns.limit_k_min0_diffrn_reflns.limit_l_max
48_diffrn_reflns.limit_l_min0_diffrn_reflns.number
28813_diffrn_reflns.pdbx_number_obs
28799#_entry.id
xxxx#_exptl_crystal.id1#_reflns_scale.group_code
1#_symmetry.entry_id
xxxx_symmetry.space_group_name_H-M'P 21 21 21'_symmetry.Int_Tables_number
19
#
loop_
_symmetry_equiv.id_symmetry_equiv.pos_as_xyz
1 'X, Y, Z'
2 'X+1/2, -Y+1/2, -Z'
3 '-X, Y+1/2, -Z+1/2'
4 '-X+1/2, -Y, Z+1/2'
#
#
loop_
_refln.crystal_id_refln.wavelength_id_refln.scale_group_code_refln.index_h_refln.index_k_refln.index_l_refln.status_refln.F_meas_au_refln.F_meas_sigma_au_refln.intensity_meas_refln.intensity_sigma_refln.pdbx_I_plus_refln.pdbx_I_plus_sigma_refln.pdbx_I_minus_refln.pdbx_I_minus_sigma_refln.pdbx_F_plus_refln.pdbx_F_plus_sigma_refln.pdbx_F_minus_refln.pdbx_F_minus_sigma_refln.pdbx_anom_difference_refln.pdbx_anom_difference_sigma
1 1 1
0
0
6 o 1376.410 15.01046 10408.40 226.5000 10408.40
226.5000 10408.40 226.5000 1376.410 15.01046 1376.410 15.01046 0.000000
0.000000

1 1 10
0
8 o 217.3632 2.853964 259.2000 6.800000 259.2000
6.800000 259.2000 6.800000 217.3632 2.853964 217.3632 2.853964 0.000000
0.000000
1 1 1
00
10 o 106.2069 3.010540 62.00000 3.500000 62.00000
3.500000 62.00000 3.500000 106.2069 3.010540 106.2069 3.010540 0.000000
0.000000
1 1 1
00
12 o 429.4464 5.076715 1011.800 23.90000 1011.800
23.90000 1011.800 23.90000 429.4464 5.076715 429.4464 5.076715 0.000000
0.000000...
#END
data_rxxxxAsf#_entry.id xxxx#
_diffrn.id 1_diffrn.crystal_id 1_diffrn.details;scalepack unmerged intensities;#_exptl_crystal.id 1#_diffrn_radiation.diffrn_id 1_diffrn_radiation.wavelength_id 1_diffrn_radiation_wavelength.id 1_diffrn_radiation_wavelength.wavelength 1.5418#
loop__diffrn_refln.diffrn_id_diffrn_refln.wavelength_id_diffrn_refln.standard_code_diffrn_refln.scale_group_code_diffrn_refln.id_diffrn_refln.index_h_diffrn_refln.index_k_diffrn_refln.index_l_diffrn_refln.intensity_net_diffrn_refln.intensity_sigma
1 1 1 1 1
0
0
6 10072.3 319.8
1 1 1 1 2
00
-6 10746.7 320.8
1 1 1 1 3008253.1 9.5
1 1 1 1 4
0
0-8
265.6 9.8...
# END OF REFLECTIONS

1

E. Krissinel and K. Henrick (2005). Detection of Protein Assemblies in Crystals. In: M.R.
Berthold et.al. (Eds.): CompLife 2005, LNBI 3695, pp. 163--174. Springer-Verlag Berlin
Heidelberg.
2
Henrick, K., and J. M. Thornton. 1998. PQS: a protein quaternary structure file server.
Trends. Biochem. Sci. 23:358-361.
3
Structure quality and target parameters. R. A. Engh and R. Huber. International Tables for
Crystallography (2006). Vol. F, ch. 18.3, pp. 382-392
4"New Parameters for the Refinement of Nucleic Acid Containing Structures." Gary
Parkinson, Jaroslav Vojtechovsky, Lester Clowney, Axel Brunger*, and Helen M. Berman.
(1996) Acta Cryst. D 52, 57-64

5"PHI/PSI- Chology: Ramachandran revisited. " GJ Kleywegt and TA Jones (1996) Structure
4, 1395-1400.
6
See Matthews, B.W. 1968. Solvent content of protein crystals. J. Mol. Biol. 33: 491-497 andhttp://www.doe-mbi.ucla.edu/~sawaya/tutorials/Characterize/characterize.html